Method and device for extracting contaminated air by suction

ABSTRACT

In a method of removing contaminated air by suction, ejector air is blown towards a tangentially directed inlet slot (3) in a cylinder (2a) comprising part of an air extractor (1). The contaminated air is entrained in this way to form a rotating air stream in the interior of the cylinder, said air stream also being imparted an axial movement component as a result of underpressure prevailing in the interior of the cylinder. The cyclone effect of the air stream in the cylinder is used to separate contaminated particles from the air and to deposit the particles on the inside of the cylinder. The air stream can also be caused to pass through a cylindrical filter (11) arranged centrally in the cylinder (2a). Blow-openings (8) for ejector air are suitably located in the vicinity of the end of a tangentially directed cylinder-extension portion (2b). The cylinder can be flushed to remove adhering particles therefrom, e.g. by means of a nozzle which is arranged in the slot (3) and which delivers a tangentially directed stream of liquid.

The present invention relates generally to a method of extractingcontaminated air by suction, and to an extractor for carrying out themethod. Extractors for this purpose find a wide field of use. Forexample, they can be used in domestic kitchens, in field kitchens andindustrial kitchens; in laboratories, and in different industrialapplications, such as for extracting impure air from spray booths, andfrom the vicinity of work benches at which harmful substances are givenoff; in plants where dust-laden goods are transported and handled; andin connection with metal baths which give off harmful vapours; andwithin the process industry etc.

Previously known extractors normally comprise a hood which permitseffective capture of the contaminated air. Normally, the air is conveyedfrom the extractor through a system of passages, by means of anextractor fan.

When the air contaminants have the form of particles or aerosols, it isdesirable, and in many cases necessary, to filter the air afterextraction, in order to prevent clogging of the said passage system andto prevent said contaminants from being discharged to atmosphere.

In extractors of the aforementioned kind, the speed at which the air iscaptured decreases inversely proportional to the square of the distanceto the suction opening. At a distance of one diameter from a circularsuction opening, the speed of the air seen in an axial direction willhave fallen to about 8% of the speed of said air at the suction opening.

In the case of processes which result in the contamination of thesurrounding air and which, at the same time, produce heat, theextractors may include so-called overhead hoods which are located abovethe source of contamination, whereat the thermal lifting force of theair is utilized to facilitate the extraction thereof. Since thesurrounding air is admixed with the upwardly approaching contaminatingair, the cross-sectional area of the air flow will increase with anincrease in distance from the contaminating source.

An empirical formula often used in these connections states that theoverhang of the hood above the contaminating source shall correspond toapproximately 1/3 the distance from said source. Known extractors whichinclude overhead hoods therefore require a lot of space.

A further, serious problem connected with overhead hoods is that thecontaminated air often passes the breathing zone of a person present inthe vicinity of the contaminating source, before the air reaches thesuction opening.

One example of a known suction extractor comprising a large and bulkyoverhead hood is described and illustrated in the U.S. Pat. No.3,221,635 (Hill). This patent can be said to describe a method ofremoving contaminated air by suction, in which the impure air is drawntangentially into a cylinder via an inlet gap or slot. In the interiorof the cylinder, the air stream is caused to rotate and, by applying anunderpressure, is given an axially directed movement and led away fromthe cylinder. The effective use of this apparatus also relies on thethermal lifting force of the heated air, i.e. the apparatus can not, forexample, be used for extracting contaminated gases by suction from aspray booth or the like where no rising air currents occur.

The Swedish published specification 76 11472-7 (publication number409.178) describes an air extractor which operates on the suctionprinciple but in which the contaminated air is not caused to pass aninlet gap and, as a rule, is not imparted a rotary movement having anaxial movement component. The extractor according to this patent,however, requires a relatively large installation space.

The object of the present invention is to provide a method and anextractor for removing contaminated air by suction, which reduces oreliminates the disadvantages of known methods and extractors.

In its widest aspect the method according to the invention is mainlycharacterised in that ejector air is blown towards the inlet gap or slotin a manner such as to entrain impurified air therewith and to admixsaid air with the air stream rotating in the cylinder.

When applying the method according to the invention, the entrained,contaminated air stream is caused to rotate at high speed within thecylinder. The cyclone effect thus produced is used for separatingparticulate contaminants from the air stream and for depositing saidcontaminants onto the inner surfaces of the cylinder. Consequently, themethod according to the invention functions equally as effectively,irrespective of whether the entrained, contaminated air is heated ornot. Further, the method permits the extractor cylinder and the blowopenings through which ejector air is blown to be placed in the desiredlocation, depending on the circumstances. Thus, the ejector air mayeither have a vertical or a horizontal direction, or may have anydesired direction relative to the horizontal or vertical plane.

For the purpose of filtering the air flowing through the cylinder, thecylinder may be provided with a filter, preferably a cylindrical filter,arranged centrally in the cylinder. Subsequent to passing the filter,the air flow will, in many cases, have lost a major part of its rotarymovement component, i.e. the air stream will move substantially in anaxial direction after passing the filter. A cylindrical filter presentsa substantially larger filter surface than does a flat filter, which isthe normal form of filter used in air extractors of the kind mentioned.

A particular advantage afforded by a filter arrangement of the kindmentioned is that the aforementioned cyclone effect cause particles ofgrease, fat and the like to be deposited on the inner surfaces of thecylinder, so that said particles do not clog or dirty the filter, thusextending the service life of the filter, before needing to be changedand cleaned. Further, if desired, the filter may comprise an activatedcarbon such as to absorb obnoxious and/or harmful gases in the airstream, which has been purified of fat particles and the like. Theseparticles of fat or grease would otherwise clog the carbon filter andrapidly make it ineffective.

The outlet opening from the cylinder may be located in the centre of,e.g., one of the end walls of the cylinder. As a result of the rotarymovement of the air within the cylinder, there is obtained a uniformsuction speed in the suction slot, even if the cylinder is relativelylong. In the case of bench-working locales, large kitchens and the like,the cylinder is placed in a horizontal position, suitably against a walland approximately at head-height over the working place in question. Inthis case, the suction slot is suitably located adjacent the wall, sothat the contaminated air is caused to move in a direction away from thebreathing zone of the workman in question.

When the cylinder is placed horizontally, with the inlet slot arrangedadjacent a wall, or adjacent a vertical extension of the wall of thecylinder (as hereinafter described) tangentially into the cylinder-theblow-openings are located adjacent said wall or said cylinder-wallextension. The ejector air is then suitably blown along the wall or theextended part of said cylinder wall, which provides for good stabilityand a favourable flow direction of the entrained contaminated air.

For reducing the extent to which air present on the sides of thecylinder is entrained into the cylinder by the ejector air, and toprevent the occurrency undesirable, disturbing air streams in saidlocale, the cylinder is suitably provided with side walls. Tests haveshown that these walls should be so formed that, when the cylinder ispositioned horizontally, the leading edge of the walls extends obliquelyupwardly from the blow-openings to the opposite peripheral portion ofthe cylinder at the wall of the ejector.

In order to obtain the best purifying effect from the extractor, it ispreferred, when applying the method of the invention, that the width ofthe inlet slot is adjusted in dependence on the underpressure in thecylinder. It is often sufficient to adjust the width of said slot whentrimming and balancing the extractor for a given locale. It ispreferred, however, that the gap-setting means can be activated fromoutside the cylinder, to enable the slot width to be readily adjusted,or finely adjusted, when required by existing circumstances.

When applying the method of the invention, a tangentially directedstream of liquid can be injected into the slot, for flushing awaycontaminating particles adhering to the inner wall of the cylinder. Thecontaminated liquid is then carried away through drainage means arrangedin the cylinder. When the cylinder is to be positioned horizontally, adrainage pipe is suitably arranged at the bottom of the cylinder.

Although the cleaning liquid can be continuously fed to the cylinder, itis preferred that the supply of said liquid is effected intermittently.Thus, for example, such a cylinder-cleaning operation can beautomatically initiated when the extractor is switched off, i.e. at theend of a working day.

Alternatively, contaminants can be removed from the cylinder, forexample, via a drainage opening provided with a closure valve andarranged in one end wall of the extractor.

One further advantage is that when a filter is arranged in theextractor, said filter can be flushed from one side, without it beingnecessary to remove the filter from the cylinder. This greatlyfacilitates cleaning of the filter, which is otherwise particularlytroublesome, for example, in large kitchens, restaurants and the like.

When the blow-openings have the form of ejector slots, the air blownfrom said slots obtains an angle of propagation of about 15° from thewall or the cylinder-wall extension. It is therefore important that theimpulse of the applied ejector air, the distance between ejector andinlet slot and the diameter of the suction cylinder are given optimalvalues.

It has been found that the diameter of the cylinder should correspond toor exceed half the distance between the ejector slots and the suctionslots. The magnitude of the ejector flow is dependent on the speed atwhich the air is blown out and the distance to the suction slot.

The invention also relates to an air extractor whose essentialcharacterizing features are disclosed in the accompanying claims.

Further aspects of the invention will be evident from the followingdescription, which is made with reference to the accompanying drawingsand which schematically illustrate a number of embodiments of theinvention. In the Figures, corresponding elements have been identifiedby the same references.

FIGS. 1-4 illustrate the principle embodiment of an air extractoraccording to the invention, whereat FIG. 1 is a front view of theextractor and FIG. 2 is a sectional side view thereof with the sidewalls removed. FIGS. 3 and 4 show the air extractor with the side wallsattached thereto, from different directions and in perspective.

FIGS. 5-7 illustrate a modified embodiment, inter alia provided with acylindrical filter. Thus, FIG. 5 is a perspective view of the extractorwith one side wall removed, FIG. 6 is a cut-away front view of theextractor and FIG. 7 is a side sectional view through the extractor.

FIGS. 8-11 are perspective views illustrating a number of different waysin which an air extractor according to the invention can be used.

FIGS. 1-4 illustrate the principal embodiment of an air extractor 1 forremoving contaminated air by suction. The extractor is intended toco-act with an underpressure-generated means (not shown), such as asuction fan, for drawing contaminated air into the extractor.

The air extractor 1 comprises a hollow cylinder having a wall 2a whichmerges with a tangentially directed cylinder-wall extension 2b. Betweenthe inner end of the cylinder wall 2a and the extension 2b there islocated an inlet slot 3 through which air is drawn tangentially into thecylinder.

Adjacent the end of the cylinder-wall extension 2b is an air-supplypassage 7 having outwardly directed blow-openings 8, through whichstreams of air are blown towards the slot 3, said air streams entrainingcontaminated air therewith.

In FIGS. 3 and 4 the air extractor is shown to be provided with sidewalls 4 and 5, of which one wall, namely 4, exhibits an axially directeddischarge opening 6, which, in practice, is suitably connected to adischarge passage.

As contaminated air enters the extractor, said air is imparted a rotarymovement, and the cyclone effect herewith produced is utilized inseparating contaminating particles from the air flow, said particlesbeing deposited on the inside of the cylinder. The incoming air flowthen departs in an axial direction through the discharge passage 6.

The width of the inlet slot 3 can be adjusted by means of screws 2caccessible from outside the cylinder wall 2a.

The reference 2d identifies a means for spraying or injecting a streamof liquid tangentially into the slot 3. Said means may have the form ofa liquid-supply pipe having a plurality of tangentially directed nozzlesarranged in said slot. Arranged at the bottom of the cylinder is adrainage pipe 2e, for conducting away contaminated liquid.

FIGS. 5-7 illustrate an example of a modified air extractor. The patternof air flow is illustrated in the different Figures by means of arrows,whereat the arrows P₁ identify the air streams blown out from theair-supply passage 7; the thinner arrows P₂ identify the entrainedcontaminated air; and the arrows P₃ within the cylinder identify thetotal air flow rotating in the cylinder.

In this embodiment there is provided a cylindrical filter 11 which islocated within the cylinder and which is arranged to be graduallythrough-passed by the rotating air flow when it has lost the major partof its energy of rotation, whereat the contaminating particles aredeposited on the filter. The purified air flow then passes axially tothe discharge passage 6a through the opening 6. The filter 11 is carriedby holder means 10 arranged in the cylinder. The end of the cylinderopposite the opening 6 is covered by a removable cover 12, which can bereadily removed to enable the filter located within the cylinder to becleaned.

The filter 11 may suitably comprise activated carbon. Since particles offat or grease present in the contaminated air are deposited, as a resultof the cyclone effect, on the inside of the cylinder wall, saidparticles will not clog or dirty the filter, thereby leaving the filterin a condition in which it is fully capable of cleansing the entrainedcontaminated air of gases present therein.

Cleaning liquid may also, in this embodiment, be introduced into thecylinder through the suction slot 3, for the purpose of cleaning theinterior of said cylinder. Contaminants taken up by the liquid can beflushed out via a drainage pipe 15 provided with a closure valve 16 inthe cylinder end-wall in which the discharge opening 6 is arranged.

In the illustrated embodiment, the supply passage 7 for ejector aircomprises a bent part of the cylinder-wall extension 2b. Ejector air issupplied by means of a fan not shown. The blow-openings 8 comprisesopenings arranged in a wall of the passage 7. These openings 8 may,optionally, merge with one another to form a slot (not shown). It willbe understood that ejector air can be supplied and blown out in otherways than those illustrated in FIGS. 5-7.

Experiments have shown that the diameter of the cylinder should exceedhalf the distance between the openings 8 and the inlet slot 3. Inaddition, the side walls should have the form of the side wall 4illustrated in FIGS. 5 and 7.

FIGS. 8-11 illustrate further examples of applications of the invention.Thus, FIG. 8 illustrates a working table 20 at which activities may takeplace which result in contamination of the surroundings, e.g. suchactivities as welding, brazing, the cleansing of dust-laden articles andequivalent working operations. The air extractor 1 is, in this case,placed horizontally at one end of the table, whereat the upper surfaceof the table itself forms a restricting wall which contributes toconducting impurified air into the inlet slot 3.

Arranged at the other end of the table is a supply passage 7 havingopenings arranged therein and being intended for blowing towards theslot streams of air which entrain therewith contaminated air at thecentral part of the table.

FIG. 9 illustrates a practical application of the air extractor shown inFIGS. 1-4 in a large kitchen, whereat the actual length of the extractor1 corresponds to the distance covered by a plurality of mutuallyadjacent cookers 21. This embodiment exemplifies the use of theextractor over a contaminating source having a heated surface, in whichcase the thermal rising force of the impurified air can be used, whereatthe blow-openings for ejector air can normally be smaller than in othercases.

FIG. 10 illustrates a vertical arrangement of an air extractor having acorresponding supply passage for blowing out entrainment air. Thearrangement can also be used in many different connections, asexemplified by a newspaper-line 22 illustrated in FIG. 10, from which itis desired to remove surplus solvent applied during a printingoperation.

A similar vertical arrangement may be used, for example, when verticallytransporting different kinds of dust-laden or particle-laden substances.

The lower part 2c of the air extractor is of conical configuration andserves to collect the contaminating particles dispersed as the airstream rotates. Thus, the process can be considered to correspond to acyclone separation process. The purified air flow is discharged upwardlyvia the connected passage 6a.

FIG. 11 illustrates the application of an air extractor 1 at a workingsite having a table surface 23 which, for example, may comprise thebottom surface of a fume cupboard or the like. Adjacent the side wall 5of the extractor is a fan housing 24 which accommodates a fan forsupplying air to a supply pipe 7 having upwardly facing blow-openings 8arranged therein. The Figure illustrates how a fluorescent tube can bemounted adjacent the extractor, for effectively illuminating the workingarea without risk of the tube being dirted to any appreciable extent bythe contaminated air. The entrained fresh air, here symbolized by thearrows P₂, passing the tube 25 contributes, in this respect, to preventdirtying of the tube to any great extent.

The aforedescribed examples of the modes of use of the method accordingto the invention and the extractor for carrying out the method will showthat the invention can be applied in many different connections, whereatparticularly effective suction can be created, despite the fact that theextractor itself is of a very simple design and has but smalldimensions. Even though in all the illustrated embodiments the airstream is discharged axially from one end of the extractor, it will beunderstood, particularly in the case of relatively long extractors, thatin certain cases it may be convenient to provide both ends of theextractor and/or intermediate parts thereof with discharge openings 6connected to one or more discharge lines 6a. The fact that the airextractor has a given axial length enables contaminated air to beremoved by suction in a uniform and steady stream, without the formationof eddy-currents externally of the extractor. When using a cylindricalfilter in the air extractor an additional important advantage isprovided in relation to known air extractors having flat filters, namelythat the rotary air stream provides for uniform distribution of thecontaminated particles on the filter, thereby enabling the greatestpossible filter area to be used, this area being great in relation tothe total space required by the air extractor.

I claim:
 1. An air extractor for removing contaminated air by suctionand arranged to co-act with an air suction device, said extractorcomprising: a hollow cylinder having a peripherally arranged inlet slotfor directing contaminated air tangentially into said cylinder, saidcontaminated air forming part of an air stream imparted a rotarymovement having an axially directed movement component within saidcylinder; discharge means for leading said air stream away from saidcylinder; ejector blow-openings arranged opposite said inlet slot forblowing streams of air towards said slot, said streams entraining therewith contaminated air, and carrying said air to the air stream rotatingin the cylinder; and a tangentially directed wall extension which mergeswith a wall of said hollow cylinder in the region of said inlet slot andextends to said ejector blow openings, said tangentially directed wallextension contributing to leading the contaminated air into said inletslot.
 2. An extractor according to claim 1, characterised in that thecylinder is provided with means for mounting a cylindrical filtertherein.
 3. An extractor according to claim 1, wherein the rotarymovement of said contaminated air causes contaminating particles toadhere to the inside of the cylinder; and further comprising spray meanslocated in the inlet slot for delivering a tangentially directed streamof liquid to the interior of said cylinder, said stream of liquid beingarranged to remove and entrain therewith said contaminating particlesadhering to the inside of the cylinder; and drainage means forconducting contaminated liquid away from the cylinder.
 4. An extractoraccording to claim 1, further comprising walls provided at the ends ofthe hollow cylinder, whose leading edges extend obliquely from theregion of said blow-openings to the peripheral portion of the hollowcylinder located adjacent said inlet slot.
 5. An air extractor forremoving contaminated air by suction and arranged to co-act with an airsuction device, said extractor comprising: a hollow cylinder having aperipherally arranged inlet slot for directing contaminated airtangentially into said cylinder, said contaminated air forming part ofan air stream within said cylinder imparted a rotary movement having anaxially directed movement component; discharge means for leading saidair stream away from said cylinder; and ejector blow-openings arrangedopposite said inlet slot for blowing streams of air towards said slot,said streams entraining there with contaminated air, and carrying saidair to the air stream rotating in the cylinder; and adjustment meansaccessible from outside the cylinder for regulating the size of theinlet slot.
 6. A method of removing contaminated air havingcontaminants, the method comprising the steps of:entraining contaminatedair in a flow of ejector air directed towards an inlet slot provided atthe periphery of a generally hollow cylindrical fixture, said generallyhollow cylindrical fixture having a wall thereof in the region of theinlet slot merging with a tangentially directed wall extension whichextends from the wall of the cylindrical fixture to a source of theejector air and contributes to leading the contaminated air into saidslot; causing mixed ejector and contaminated air to pass through saidinlet slot into said hollow cylindrical fixture, the introduction ofsaid mixed air into said hollow cylindrical fixture through said inletslot causing the mixed air to rotate within said cylindrical fixture inorder to impart centrifugal force to the contaminants; and withdrawingthe rotating mixed air stream axially from the hollow cylindricalfixture.
 7. A method according to claim 6, wherein the rotation of themixed air within said hollow cylindrical fixture creates a cycloneeffect causing the contaminants to be separated and deposited around aninner surface of said hollow cylindrical fixture.
 8. A method accordingto claim 6, further comprising the step of filtering the mixed air as itmoves through the hollow cylindrical fixture.
 9. A method according toclaim 6, wherein said flow of ejector air is provided by an air ejectorhaving blow openings directed toward said inlet slot.
 10. A methodaccording to claim 1, further comprising the steps of:flushingcontaminants from the inner surface of the hollow cylindrical fixture;and draining the contaminants from the hollow cylindrical fixture.
 11. Amethod of removing contaminated air having contaminants, the methodcomprising the steps of:entraining contaminated air in a flow of ejectorair directed towards an inlet slot provided at the periphery of agenerally hollow cylindrical fixture; causing mixed ejector andcontaminated air to pass through said inlet slot into said hollowcylindrical fixture, the introduction of said mixed air into said hollowcylindrical fixture through said inlet slot causing the mixed air torotate within said cylindrical fixture in order to impart centrifugalforce to the contaminants; withdrawing the rotating mixed air streamaxially from the hollow cylindrical fixture; and adjusting the size ofthe inlet slot in order to maintain a desired underpressure within thehollow cylindrical fixture.